This research examines the impact of different dietary arginine (Arg) concentrations on growth performance, carcass traits, gut morphology, and gene expression in Japanese quails aged 1 to 35 days. A total of 600 Japanese quail chicks were randomly allocated to fve dietary treatments consisting of 0.75%, 1.0%, 1.25%, 1.50%, and 1.75% digestible Arg, with six replicate cages for each treatment and 20 birds housed per cage. Dietary digestible Arg concentrations of 1.0% or above led to improvements in growth performance, with the groups receiving 1.25% and 1.50% demonstrating the most pronounced increases in body weight and average daily gain (ADG) by day 35. The group receiving 1.25% digestible Arg had the most advantageous feed conversion ratio (FCR) and showed an increase in average daily feed intake. According to the one-slope linear broken-line regression model, the estimated breakpoint for ADG was 1.19% digestible Arg, while the breakpoint for FCR was 1.30% digestible Arg. Quadratic regression analysis further estimated maximal ADG at 1.42% digestible Arg and minimal FCR at 1.47% digestible Arg during the 1–35 day period. Furthermore, the 1.25% digestible Arg diet markedly improved gut morphology, especially in terms of jejunal villus height and surface area, which suggests an enhanced capacity for nutrient absorption. The group receiving 1.25% digestible Arg demonstrated superior carcass yield, signifcantly exceeding that of the 0.75% and 1.75% groups. Gene expression analysis revealed that hepatic HSP90 expression peaked in the 1.00% Arg group, but the expression levels of hepatic target of rapamycin (TOR) and ribosomal protein S6 kinase alpha-1 (RPS6KA1) were considerably elevated in the 1.50% and 1.75% groups. The treatments with 1.25% and 1.50% digestible Arg demonstrated the highest levels of kidney HSP70 expression. In conclusion, dietary supplementation at a concentration of 1.25% and more digestible Arg improved growth performance, carcass yield, gut morphology, and expression of genes related to growth and stress in Japanese quail, with model-based estimates refning the digestible Arg requirement range between 1.19% and 1.47%.
